Slow internet initial connection

Help !   I need some suggestions about the cause of a problem that has just recently started happening

When I click on my desktop Internet Explorer 8 icon to go onto the internet, about 75% of the time nothing happens for sometimes over half a minute or more.
Then when eventually the Windows Internet Explorer window appears with the "connecting........" tab - there is another painstaking long delay until my default Google home page eventually appears
 
Having got onto a website, navigating around it is OK as regards speed, but clicking on any web link either takes ages or doesn't work at all.
 
Whilst all these delays are going on, there is an accompaning whirring sound from my hard drive as if the computer is searching for something on the disk
 
All other applications seem OK.

I have done all the usual things like get rid of unwanted files etc.. off the system even though there is plently of disk space left; have cleaned up the registry; degragmented the hard disk; run CHKDSK etc  etc...

I am running Windows XP (Media Centre edition)  on a Dell Dimension 3100 with 1GB RAM 

Other forums have suggested using a different web browser -  but this problem has only started happening in the last week and I have been browsing the web with no problems on this machine for over 3 years - so I don't think that's the answer

Could it possibly be a problem with a faulty RAM module ?? I have 2 X 512MB = 1GB

John 

John